Income Taxes - Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current taxes
U.S. income	$ 935	$ 1,076	$ 1,068
Foreign income	95	93	115
State income	32	60	49
Total taxes, current	1,062	1,229	1,232
Deferred taxes (benefits)
U.S. Income	69	22	10
Foreign income	9	(6)	(22)
State income	(4)	5	(10)
Total taxes, deferred	74	21	(22)
Total taxes	$ 1,136	$ 1,250	$ 1,210